Tape libraries have historically been the primary storage devices for amassed digital data. This has been due in part because of the tape libraries' ability to store large amounts of data in a cost-efficient and data-stable manner. Other types of storage systems containing alternative media such as disc drives, however, are beginning to gain momentum as a consequence of advancements in the technology. Disc drive-based systems generally facilitate an additional level of flexibility in the way data is stored. Depending on the configuration of the storage system, the random access functionality of disc drives can dramatically speed up data transfer between a host and storage system. Such advances are embodied, for example, in a Virtual Tape Library (VTL) which is a leading alternative to the traditional tape library.
VTLs are generally promoted as faster, more versatile backup systems than the traditional tape-based libraries. A VTL works by emulating legacy tape libraries by operating with standard tape backup software. Put simply, a VTL can be adapted to present the appearance of a tape library of almost any make and model to a host. Hence, data can be transmitted to a VTL in streaming protocol whereby data can be stored on media as a contiguous data packet emulating the linear last-in/last-stored format of tape media. Such data transmitted by a host is typically received by a buffer system in the VTL capable of accepting the data transmission at high speeds. The buffer then transmits the data at a buffered rate, typically slower, tailored for the speed at which the storage media is capable of storing the data.
In some instances, power supplying a VTL may be unexpectedly reduced to some power level less than enough for full operation of the VTL. For example, the power may be interrupted due to a power outage wherein the power is cycled from an on condition to an off condition, while data is being received by the VTL. Alternatively, a data storage system operating under the protection of fault protection circuitry may suffer variations in supplied power, such as power spikes or other undesirable power surges or conditions. The consequence of such power fluctuations may result in data being incompletely stored or even corrupted. Under these circumstances, one method of determining if stored or redundant data has been affected is to compare, on a random sample or bit-by-bit basis, all of the primary data with the redundant data (if the VTL supports redundant data capabilities), once power is fully re-supplied to the VTL. Needless to say, comparing data to find discrepancies between redundant data and primary data or the point at which data storage was terminated can often be time-consuming.
The invention described herein is generally directed to improvements to the time consuming data comparing exercise following interrupted data storage.